However, he did not disclose the total amount of the funding in the round. Some reports have said the latest round amounted to a $100 million minority investment, placing the value of the two-year-old company at close to $1 billion.

"It was important to us that we find investment partners who share our vision for building a company of enduring value," Williams said in the blog. "Twitter's journey has just begun and we are committed to building the best product, technology, and company possible. I'm proud of the team we've built so far and I'm confident in the future we'll build together."

The service has seen rapid growth in the past year. Worldwide visitors to Twitter.com hit 44.5 million in June, up 15-fold from a year earlier, according to comScore (NASDAQ: SCOR) data.

With that growth comes expenses and the investment was likely needed since Twitter has to date seemed in no hurry to monetize the site.

Co-founder Biz Stone said earlier this week that the company has no plans to introduce advertising to the site this year. Instead, Stone said the company's immediate focus was to build out features, including an improved search functions and paid-for commercial accounts.

"Any kind of approach toward advertising is going to be awhile ... We're not thinking about that just yet," Stone was quoted in a report by Reuters on his remarks at the 140: Twitter Conference in Los Angeles.

Stone did say Twitter aims to offer premium features for commercial account users this year.

"We wanted to show people that we're here to stay and here we are making money," Stone said. Among features Twitter might introduce and charge for are analytics tools that would allow companies to gather data on their followers, he said.